The U.S. Pat. No. 5,063,784 discloses a transducer assembly wherein the assembly may be easily serviced. The initial unthreading of a cartridge in the housing closes a first valve so that refrigeration fluid will not leak out of the assembly.
Other prior art using a transducer assembly to be assembled in the field to a manifold or the like first assembled a manual shut off valve to the manifold and then screwing the transducer assembly into the manual shut off valve. This was undesirable because it merely added another part to leak, especially the leakage along the valve stem of refrigerant fluid which was a danger to the ozone layer in the atmosphere. Additionally, the operator might not open the hand valve fully once the combination was assembled and this could adversely affect the pressure applied to the pressure transducer.
The prior art also utilized a pressure transducer such as a strain gage in the transducer assembly and then this change of resistance was fed out through a shielded cable to a external conditioning circuit. The cable had to be shielded because this was a high impedance circuit between the strain gage and the external conditioning circuit which was extremely sensitive and could pick up static or electromagnetic radiation.